Add a floating close button for arc custom notification

ui/arc/notification/arc_custom_notification_view.h

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef UI_ARC_NOTIFICATION_ARC_CUSTOM_NOTIFICATION_VIEW_H_
 #define UI_ARC_NOTIFICATION_ARC_CUSTOM_NOTIFICATION_VIEW_H_
 
+#include <memory>
 #include <string>
 
 #include "base/macros.h"
+#include "ui/arc/notification/arc_custom_notification_item.h"
+#include "ui/views/controls/button/button.h"
 #include "ui/views/controls/native/native_view_host.h"
 
 namespace exo {
 class NotificationSurface;
 }
 
+namespace views {
+class ImageButton;
+class Widget;
+}
+
 namespace arc {
 
-class ArcCustomNotificationView : public views::NativeViewHost {
+class ArcCustomNotificationView : public views::NativeViewHost,
+                                  public views::ButtonListener,
+                                  public ArcCustomNotificationItem::Observer {
  public:
-  explicit ArcCustomNotificationView(exo::NotificationSurface* surface);
+  ArcCustomNotificationView(ArcCustomNotificationItem* item,
+                            exo::NotificationSurface* surface);
   ~ArcCustomNotificationView() override;
 
  private:
+  void CreateFloatingCloseButton();
+
   // views::NativeViewHost
   void ViewHierarchyChanged(
       const ViewHierarchyChangedDetails& details) override;
+  void Layout() override;
 
+  // views::ButtonListener
+  void ButtonPressed(views::Button* sender, const ui::Event& event) override;
+
+  // ArcCustomNotificationItem::Observer
+  void OnItemDestroying() override;
+  void OnItemPinnedChanged() override;
+
+  ArcCustomNotificationItem* item_;
   exo::NotificationSurface* const surface_;
 
+  // A close button on top of NotificationSurface. Needed because the
+  // aura::Window of NotificationSurface is added after hosting widget's
+  // RootView thus standard notification close button is always below
+  // it.
+  std::unique_ptr<views::Widget> floating_close_button_widget_;
+
+  views::ImageButton* floating_close_button_ = nullptr;
+
   DISALLOW_COPY_AND_ASSIGN(ArcCustomNotificationView);
 };
 
 }  // namespace arc
 
 #endif  // UI_ARC_NOTIFICATION_ARC_CUSTOM_NOTIFICATION_VIEW_H_